企源知识库

Much research ( ) into the possible causes of the disease in the past few years.
A、has been done
B、was done
C、have been done
D、were done
【正确答案】：A
【题目解析】：in the past few years 一段时间，用现在完成时，句子含义是在过去一些年里，关于这种致病原因，已经做了很多相关的研究。